Azonitrile compounds are known to be useful as polymerization initiators. They are advantageous because they can be used with a higher degree of safety than peroxide catalysts and yield both performance and economic improvements over other catalysts which might be used in the same type of polymerization reaction.
Symmetrical azonitrile compounds are generally solid and have low solubility in many organic solvents, especially non-polar types, particularly at high pressures (15,000 p.s.i. and higher). Asymmetrical azonitrile compounds, on the other hand, usually have appreciably lower melting points than symmetrical azonitriles. Many asymmetrical azonitriles are liquids at room temperature and below and all tend to have much higher solubility in organic liquids. Producers of low density polyethylene have been seeking efficient and effective liquid azo polymerization catalysts for many years. While compounds such as 2,2'-azobis(isobutyronitrile) are highly effective as initiators in the production of low density polyethylene, this material is a solid which cannot be handled in the process equipment except in solution form. Under the conditions employed for the polymerization, such as, for example, elevated pressure, solid azonitriles crystallize from solution and plug the equipment. Liquid azonitriles which are as active as 2,2'-azobis(isobutyronitrile) and which have freezing points of 0.degree. C. or lower, preferably -20.degree. C. or lower, would be ideal for the production of low density polyethylene which is carried out at pressures of from about 15,000 to about 50,000 p.s.i.
The only published process for producing asymmetrical liquid azonitrile initiators involves a reaction scheme utilizing t-butylhydrazine and a ketone as reagents to which is added HCN. As described in Canadian Patent No. 924,299 issued to Ronald E. MacLeay et al. on Apr. 10, 1973, upon oxidation, the following compounds are obtained ##STR1## Such a process is costly because it is lengthy and requires the use of t-butylhydrazine which is not a common chemical. Further, compounds containing the nitrile group at both ends are not obtained by this process.